import pygame
from pygame.sprite import Sprite

class Ship(Sprite):

    def __init__(self,ai_settings,screen):
        """初始化飞船并设置其初始位置"""
        super(Ship,self).__init__()
        self.screen=screen
        self.ai_settings=ai_settings

        # 加载飞船图像并获取其外接矩形
        self.image=pygame.image.load('images\ship.bmp')
        self.rect=self.image.get_rect()
        self.screen_rect=screen.get_rect()

        # 每艘新飞船放在屏幕底部中央
        self.rect.centerx=self.screen_rect.centerx
        self.rect.bottom=self.screen_rect.bottom

        # 在飞船的属性center中存储小数值
        self.center_x=float(self.rect.centerx)
        self.center_y=float(self.rect.centery)

        # 移动标志
        self.moving_right=False
        self.moving_left=False
        self.moving_up=False
        self.moving_down=False

    def update(self):
        """根据移动标志调整飞船的位置"""
        # 更新飞船的center值，而不是rect
        if self.moving_right and self.rect.right < self.screen_rect.right:
            self.center_x += self.ai_settings.ship_speed_factor
        if self.moving_left and self.rect.left > 0:
            self.center_x -= self.ai_settings.ship_speed_factor
        if self.moving_up and self.rect.top>0:
            self.center_y -= self.ai_settings.ship_speed_factor
        if self.moving_down and self.rect.bottom < self.screen_rect.bottom:
            self.center_y += self.ai_settings.ship_speed_factor

        # 根据self.center更新rect对象
        self.rect.centerx = self.center_x
        self.rect.centery = self.center_y

    def blitme(self):
        """在指定位置绘制飞船"""
        self.screen.blit(self.image,self.rect)

    def center_ship(self,ship_height):
        """让飞船在屏幕上居中"""
        self.center_x = self.screen_rect.centerx
        self.center_y = self.screen_rect.bottom - ship_height/2